This invention generally relates to printer apparatus and methods and more particularly relates to a thermal ink jet printer having enhanced heat removal capability and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime.
An ink jet printer produces images on a recording medium by ejecting ink droplets onto the recording medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the ability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In the case of thermal inkjet printers, a print head structure comprises a single or plurality of ink cartridges each having a nozzle plate that includes a plurality of nozzles. Each nozzle is in communication with a corresponding ink ejection chamber formed in the print head cartridge. Each ink ejection chamber in the cartridge receives ink from an ink supply reservoir containing, for example, yellow, magenta, cyan or black ink. In this regard, the ink supply reservoir may be internal to the cartridge and thus define an xe2x80x9con boardxe2x80x9d or internal ink reservoir. Alternatively, each cartridge may be fed by conduit from an xe2x80x9coff-axisxe2x80x9d or remote ink supply reservoir. In either event, each ink ejection chamber is formed opposite its respective nozzle so ink can collect between the ink ejection chamber and the nozzle. Also, a resistive heater is disposed in each ink ejection chamber and is connected to a controller, which selectively supplies sequential electrical pulses to the heaters for actuating the heaters. When the controller supplies the electrical pulses to the heater, the heater heats a portion of the ink adjacent the heater, so that the portion of the ink adjacent the heater vaporizes and forms a vapor bubble. Formation of the vapor bubble pressurizes the ink in the ink ejection chamber, so that an ink drop ejects out the nozzle to produce a mark on a recording medium positioned opposite the nozzle.
During printing, the print head is moved across the width of the recording medium as the controller selectively fires individual ones of the ink ejection chambers in order to print a swath of information on the recording medium. After printing the swath of information, the printer advances the recording medium the width of the swath and prints another swath of information in the manner mentioned hereinabove. This process is repeated until the desired image is printed on the recording medium. Such thermal inkjet printers are well-known and are discussed, for example, in U.S. Pat. No. 4,500,895 to Buck, et al.; U.S. Pat. No. 4,794,409 to Cowger, et al.; U.S. Pat. No. 4,771,295 to Baker, et al.; U.S. Pat. No. 5,278,584 to Keefe, et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), the disclosures of which are all hereby incorporated by reference.
In addition, in order to increase print resolution, current practice is to place the nozzles and respective heaters relatively close together on the print head. Moreover, in order to increase printer speed, width of the printing swath is increased by including a relatively large number of nozzles and corresponding heaters in the print head. To further aid in increasing printer speed, the heaters are typically fired at a relatively high frequency.
However, it has been observed that such efforts to increase print resolution and printer speed may result in excessive heat generation in the print head. Excessive heat generation in the print head is undesirable. In this regard, bubble formation in the thermal inkjet print head is directly influenced by temperature and excessive heat generation interferes with proper bubble formation (e.g., size of vapor bubble). Also, excessive heat generation may cause the ink drop to be prematurely ejected. Premature ejection of the ink drop may in turn lead to printing anomalies (e.g., unintended ink marks) appearing on the recording medium. In addition, excessive heat generation may cause unintended vapor bubbles to accumulate in the ink, thereby blocking the exit nozzle and interfering with ejection of the ink drop when required. Further, excessive heat generation may ultimately shorten operational lifetime of the heater.
Techniques for cooling thermal inkjet print heads to reduce excessive heat generation are known. One such technique is disclosed by U.S. Pat. No. 6,120,139 titled xe2x80x9cInk Flow Design To Provide Increased Heat Removal From An Inkjet Printhead And To Provide For Air Accumulationxe2x80x9d issued Sep. 19, 2000 in the name of Winthrop Childers, et al. and assigned to the assignee of the present invention. The Childers, et al. patent discloses an inkjet printer having a print head assembly that includes a substrate. Formed on the substrate are ink ejection chambers and their respective ink ejection heater resistors. Flow directors direct ink flow onto the substrate and heat transfers from the substrate into the ink as the ink flows toward the drop ejection chambers where the warm ink is ejected onto recording media. In this manner, the flow directors help channel the ink flow path to maximize heat transfer to the ejected ink droplets. Thus, it would appear the ejected ink droplet acts as a heat sink for removing heat from the substrate and hence from the print head assembly. However, the ink droplet itself has limited capacity or capability to act as a heat sink because the volume of the ink droplet is necessarily limited. Although the Childers, et al. device performs its function as intended, it is nonetheless desirable to enhance heat removal beyond the heat removal capability afforded by the limited volume of the ejected ink droplet. Thus, enhancing heat removal in the Childers, et al. device would increase printer speed and heater lifetime.
Therefore, what is needed is a thermal ink jet printer having enhanced heat removal capability and method of assembling the printer, the printer being adapted for high speed printing and increased thermal resistor lifetime.
The present invention resides in a thermal inkjet printer having enhanced heat removal capability, comprising a thermal inkjet print head adapted to hold an ink body, the print head including a heating element adapted to be in fluid communication with the ink body; a heat removal structure in thermal communication with the heating element for transferring heat from the heating element to the ink body; and a controller coupled to the heating element.
According to an aspect of the present invention, a thermal inkjet printer includes a thermal inkjet print head adapted to hold an ink body therein. The print head comprises an ink cartridge including a heat conductive substrate and a resistive heating element coupled to the substrate. The cartridge also includes a face plate having a nozzle orifice positioned opposite the heating element. The heating element is adapted to be in fluid communication with the ink body for generating heat to heat a portion of the ink body near the heating element. A vapor bubble forms in the ink body between the heating element and the nozzle orifice when the portion of the ink body near the heating element reaches a predetermined temperature. Presence of the vapor bubble forces an ink drop out the nozzle orifice to form an image on a recording medium. A conductive heat removal structure is in thermal communication with the heating element and is also in fluid communication with the ink body. Heat is transferred from the heating element, through the substrate and into the heat removal structure. The heat removal structure then surrenders the heat to the ink body, which functions as an xe2x80x9cinfinitexe2x80x9d heat sink in order to provide enhanced heat removal.
A feature of the present invention is the provision of a heat removal structure for enhanced removal of heat generated by the heating element.
An advantage of the present invention is that printing speed is increased.
Another advantage of the present invention is that use thereof allows for proper bubble formation (e.g., size of vapor bubble).
Still another advantage of the present invention is that risk of premature ejection of ink drops is reduced.
Yet another advantage of the present invention is that risk of accumulation of unintended vapor bubbles in the ink is reduced.
Moreover, another advantage of the present invention is that use thereof prolongs operational lifetime of the heating element.